WO2011143541A2

WO2011143541A2 - Carbon fiber composite structural rod and method of manufacture

Info

Publication number: WO2011143541A2
Application number: PCT/US2011/036413
Authority: WO
Inventors: George E. Husman
Original assignee: Zoltek Companies, Inc.
Priority date: 2010-05-14
Filing date: 2011-05-13
Publication date: 2011-11-17
Also published as: WO2011143541A3

Abstract

A structural core for an electrical conductor includes an inner core of a carbon fiber composite and a protective coating bonded to and surrounding the inner core. The protective coating may include discontinuous reinforcing fibers in a polymeric matrix. Alternatively, the protective coating may be substantially free of fibers.

Description

CARBON FIBER COMPOSITE STRUCTURAL ROD

AND METHOD OF MANUFACTURE

Technical Field

The present invention relates to a carbon fiber composites, and more particularly to carbon fiber composite rods and methods for manufacturing such rods for use as structural reinforcement in high-voltage electrical transmission cables.

Background

Traditionally, overhead electrical transmission cables are constructed of a central steel core that is wrapped in an aluminum conducting layer. However, these cables are susceptible to corrosion in certain environments. Moreover, such cables are susceptible to excessive sag, which is a direct result of the temperature increase from the increasing current levels carried by these transmission cables.

More recently, carbon fiber composite cores have been introduced as the structural reinforcement in high-voltage transmission cables. Because the carbon fiber composite core has a near zero coefficient of thermal expansion, sag does not occur due to increased temperature. Furthermore, the carbon fiber composite cores have very high modulus of elasticity and zero creep under load, so that these composite cores are very efficient as structural reinforcements for transmission cables as well as other structural reinforcement applications, including underwater umbilicals and tethers for off-shore drilling platforms.

Current concepts for the carbon fiber composite cores use an outer core of continuous glass fiber (or other non-conducting continuous reinforcing fiber) composite to serve to electrically insulate the inner carbon fiber core from the aluminum conductor and metal end fittings. In addition, this outer core must transfer load from the inner core to metallic end fittings and splice fittings. The outer continuous glass fiber composite core is structurally capable of transferring load to the fittings. The outer glass fiber core also carries a percentage of the total loading in the composite core system. While this core system works well, the glass fiber is heavier and has a higher density than carbon fiber, which detracts from the overall structural efficiency of the core. Summary

In the present invention, a carbon fiber composite rod includes a tough polymer outer coating surrounding the inner carbon fiber core to provide electrical insulation from the metallic conductor and end fittings. In the carbon fiber composite rod of the present invention, there is no continuous glass fiber outer composite surrounding the inner carbon fiber core. The carbon fiber composite rod is particularly useful as structural reinforcement in high-voltage electrical transmission cables. The outer polymer coating may include a low percentage of short, discontinuous non-conducting fibers to enhance the structural properties of the coating. Alternatively, the polymer coating may not be reinforced and contains no reinforcing fibers. The carbon fiber inner core of the present invention carries all of the structural load of the cable and the outer polymer coating provides only electrical insulation. The present invention provides a cost effective method for uniformly coating the carbon fiber composite core with a polymer coating to provide a composite rod than can effectively transfer load from the core to metallic end fittings.

In a first aspect of the invention there is provided a core for an electrical conductor that includes an inner composite core of continuous carbon fibers embedded in a polymeric matrix; and a protective polymeric coating bonded to and surrounding the inner composite core. The inner composite core is substantially free of continuous fibers that are different from carbon fibers, such as continuous glass fibers.

In another aspect of the invention there is provided a power transmission conductor that includes an inner composite core of continuous carbon fibers embedded in a polymeric matrix; a protective polymeric coating bonded to and surrounding the inner composite core; and a plurality of electrically conductive rods wound around the protective coating. The inner composite core is substantially free of continuous fibers different from carbon fibers. In one embodiment, the electrically conductive rods include aluminum or an aluminum alloy.

In a further aspect of the invention, there is provided a carbon fiber composite structural rod that includes an inner composite core of continuous carbon fibers embedded in a polymeric matrix; and a protective polymeric coating bonded to and surrounding the inner composite core. The inner composite core is substantially free of continuous fibers that are different from carbon fibers, such as continuous glass fibers. In one embodiment, the inner composite core of the structural rod may include a continuous central bore. The central bore may be filled with a nonstructural filler, such as foam.

In one embodiment, the polymeric matrix of the inner composite core is a thermosetting polymer, preferably an epoxy. In another embodiment, the polymeric matrix of the inner composite core is a thermoplastic polymer.

The protective polymeric coating that surrounds the inner composite core may be a thermoplastic polymer or a thermosetting polymer. In one embodiment, the protective polymeric coating is substantially free of reinforcing fibers. In another embodiment, the protective polymeric coating is a thermoplastic polymer matrix with randomly oriented, non-conductive reinforcing fibers embedded in the thermoplastic polymer matrix. The reinforcing fibers may be, for example, glass fibers or aramid fibers.

The thickness of the outer protective coating may be in the range of about 0.01 inch (0.25 mm) to about 0.1 inch (2.5 mm).

In one embodiment, the tensile strength of core is at least 250,000 psi (1723

MPa).

In yet another aspect of the invention there is provided a method of forming a core for an electrical conductor. The method includes the steps of forming an inner composite core from a plurality of continuous carbon fibers embedded within a resin matrix; at least partially curing the resin matrix; applying a coating of a polymeric material to the inner composite core. The method may further include the step of curing the polymeric material to form a protective coating.

The inner composite core may be formed by a pultrusion process. The polymeric material of the protective coating may be applied using a wire coating process.

These and other features of the carbon fiber composite rod are fully described and particularly pointed out in the claims. The following description and annexed drawings set forth in detail certain illustrative embodiments, these embodiments being indicative of but a few of the various ways in which the principles may be employed. Brief Description of the Drawings

Figure 1 is a fragmentary perspective view showing a first embodiment of a composite reinforcing rod having an inner composite core and a protective coating surrounding the inner composite core.

Figure 2 is a fragmentary perspective view showing another embodiment of a composite reinforcing rod having an inner composite core and a fiber filled protective coating surrounding the inner composite core.

Figure 3 is a fragmentary perspective view showing an embodiment of a composite reinforcing rod having an inner composite core and a protective coating surrounding the inner composite core, where the inner core has a central bore.

Figure 4 is a cross-sectional view of a power transmission conductor including trapezoidal aluminum wire in accordance with the present invention.

Figure 5 is a photograph showing a cross-section of a composite reinforcing rod having an inner composite core of continuous carbon fibers embedded in a polymeric matrix and an outer protective coating of a thermoplastic polymer that is free of reinforcing fibers.

Figure 6 is a photograph showing a cross-section of a composite reinforcing rod having an inner composite core of continuous carbon fibers embedded in a polymeric matrix and an outer protective coating of a thermoplastic polymer that contains 40% by weight of discontinuous glass reinforcing fibers.

Figure 7 is a photograph showing a cross-section of a composite reinforcing rod having an inner composite core of continuous carbon fibers embedded in a polymeric matrix and an outer protective coating of a thermoplastic polymer that contains 20% by weight of discontinuous glass reinforcing fibers.

Figure 8 is a photograph showing the outer surface of a protective coating of thermoplastic polymer that is free of reinforcing fibers.

Figure 9 is a photograph showing the outer surface of a protective coating of thermoplastic polymer that contains discontinuous glass reinforcing fibers.

Figure 10 is cross-sectional view of a coated composite reinforcing rod within an end fitting member.

Figure 1 1 is a photograph of a coated composite reinforcing rod with end fixtures attached prior to load transfer testing.

Figure 12 is a photograph of the coated composite reinforcing rod after load transfer testing. Detailed Description

The structural support rod of the present invention is particularly useful for applications as a core or structural carrier for electrical transmission cables. In a first embodiment of the invention, there is provided a core for an electrical conductor that includes an inner composite core of continuous carbon fibers embedded in a polymeric matrix, and a protective polymeric coating surrounding the inner composite core.

Referring to FIG. 1 , a carbon fiber composite structural rod 10 includes an inner composite core 12 made from continuous carbon fibers embedded in a polymeric matrix. A protective polymeric coating 14 surrounds the inner composite core 12.

The carbon fiber composite inner core 12 contains uni-directional carbon fibers embedded in a polymer matrix resin that can be a thermosetting polymer or thermoplastic polymer. The carbon fibers extend substantially in parallel and longitudinally along the length of the inner core 12. The inner composite core 12 may be manufactured by a pultrusion process that is widely known in the composites industry. The performance characteristics and use temperature of the inner composite core are dependent on the end user requirements.

In one embodiment, the carbon fiber structural rod 10 is capable of meeting the structural loading and other requirements for reinforcement of electrical transmission cables. These requirements include high longitudinal tension loading for long periods of time without creep, fatigue resistance under cyclic loading, and structural performance at elevated temperatures (i.e., 200°C and higher). Carbon fibers useful for electrical transmission cable applications preferably have a coefficient of thermal expansion that is about 0 or less than 0. In addition, the carbon fibers preferably have a tensile strength of between about 350,000 psi (2412 MPa) to about 700,000 psi (4823 MPa).

In a preferred embodiment, the carbon fiber of the inner composite core includes Panex^® 35, a 50,000 filament commercial carbon fiber tow, produced by Zoltek Corporation. The typical properties reported for this fiber are as follows:

Tensile Strength = 550,000 - 600,000 psi (3789 - 4134 MPa)

Tensile Modulus = 35.5 - 36.0 million psi (244.5 - 248.0 GPa)

Density = 0.065 pounds/inch³ (1 .80 g/cm³)

Coefficient of Thermal Expansion = - 0.75 x 10^"6 / °K The elevated temperature performance of the composite rod is dependent on the matrix resin used in the composite rod. There are several classes of polymers that provide retention of properties within the desired temperature range. For use in electrical transmission cables, for example, the use temperature of the matrix resin would be in the range of about 150° to about 250°C. In one embodiment, the minimum temperature requirement for the matrix resin of the inner core is about 200°C.

Useful thermosetting polymers include epoxies, which can readily be used in pultrusion processing and have been formulated into composite matrix resin systems with excellent property retention at 200°C. Other useful thermosetting polymers include bismaleimides, urethanes, phenolics, and polyimides. In a preferred embodiment, the matrix resin of the inner composite core 12 is a high temperature epoxy. Useful thermoplastic polymers include polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyetherimide (PEI), thermoplastic polyimide, and other similar high temperature thermoplastic polymers. For pultrusion processing of the continuous carbon fibers, thermoset polymers as the matrix resin are preferred.

The inner composite core may include carbon fibers having at least 50% volume fraction within the polymer resin and preferably at least 60% volume fraction.

In general, a higher volume fraction of fibers in the composite core results in a higher performing composite. In one embodiment, the volume fraction of carbon fibers embedded in the polymer matrix is in the range of about 65% to about 72%.

In one embodiment, the polymer resin of the inner composite core includes a high temperature epoxy resin produced by Momentive Performance Materials, Inc. having the designation Momentive Epoxy Research Resin RSL-3896 with LS-252V curing agent. This matrix resin system has a reported glass transition temperature

(Tg) of 210 - 220°C and reported retention of properties up to 200°C.

The carbon fiber reinforced composite rod produced in accordance with the present invention possesses the desired properties of excellent fatigue behavior, creep resistance, and near zero thermal expansion. In the manufacturing process, the carbon fibers are fully wetted with the matrix polymer to provide good bonding and load transfer within the composite, and there are no significant voids within the composite.

The ability of the carbon rod to carry a specific tension load in pounds force will be directly dependent on the cross-sectional area of the rod, the strength property of the carbon fiber used, and the fiber volume content of the carbon fiber in the rod. In one embodiment, the tensile strength of carbon rod is at least 250,000 psi (1723 MPa). Preferably, the tensile strength of the carbon rod is at least 300,000 psi (2067 MPa), or at least 350,000 psi (2412 MPa). The strength of a carbon fiber reinforced composite rod in pounds per square (psi) inch can easily be estimated by using the simple rule of mixtures: composite strength = fiber strength x fiber volume fraction + resin matrix strength x resin volume fraction. For further simplification, the strength contribution of the much lower strength matrix resin may be ignored. As an example, a composite rod containing carbon fiber having a certified tensile strength of 600,000 psi (4134 MPa) with a fiber volume content of the composite rod of 70% would have an estimated maximum strength of the composite rod of: 600,000 psi x 0.70 = 420,000 psi (2894 MPa).

For a specific load carrying requirement in pounds force, the required rod area and diameter can be calculated. As an example, if the load requirement is 20,000 pounds, the calculated rod area = 20,000 pounds / 420,000 psi = 0.0476 inch². Thus the calculated diameter would be 0.246 inch (6.25 mm).

The protective polymeric coating 14 provides environmental and handling protection to the carbon composite core 12. In electrical transmission cable applications, the polymeric coating provides a layer for load introduction through mechanical end fittings and splicing concepts, and provides electrical isolation of the carbon fibers from metallic end fittings and splices. The polymeric coating also provides electrical isolation from the metallic conductor of the transmission cable to prevent galvanic corrosion. The thickness of the polymeric coating may be in the range of about 0.01 inch (0.25 mm) to about 0.1 inch (2.5 mm). In one embodiment, the thickness of the protective polymeric coating is in the range of about 0.02 inch (0.5 mm) to about 0.08 inch (2.0 mm); or in the range of about 0.02 inch (0.5 mm) to about 0.04 inch (1 .0 mm).

The protective polymer coating 14 that surrounds the inner composite core 12 may be a thermoplastic or a thermosetting polymer. In a preferred embodiment, the protective polymer coating includes a thermoplastic polymer that provides a tough and durable protective layer over the carbon composite inner core and is resistant to cracking. The thermoplastic coating can be applied in a manufacturing operation using a hot melt process without the need for chemical curing. For example, the protective coating material may be applied in a wire-coating process. During high- speed wire coating, melt emerges from an annular die and is drawn onto the inner core by a vacuum, applied inside the annular extrudate, or melt cone. This process can either be done as a high speed secondary process or done in-line with the pultrusion process described above with reference to the carbon composite core. Other manufacturing processes, including, but not limited to spraying, dipping or powder coating may also be used to apply the polymer coating. To meet the 200°C temperature requirement for the electrical transmission cable application, the thermoplastic polymer may be selected from several high temperature polymers, including polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyetherimide (PEI), or other similar high temperature thermoplastic polymers. In a preferred embodiment, the protective polymer coating includes polyphenylene sulfide (PPS), which is cost effective, retains its properties at high temperature, is chemically resistant and is compatible for bonding to an epoxy containing carbon composite inner core.

The protective polymeric coating 14 that surrounds the inner composite core may alternatively be formed of a thermosetting polymeric material that is applied to the inner composite core, and then cured to form the protective coating. Non-limiting examples of such thermosetting polymers include polyesters, polyimides, epoxies, phenolics and polyurethanes.

The protective polymeric coating 14 may or may not include discontinuous or chopped, non-conductive reinforcing fibers dispersed within the polymer material. In a preferred embodiment, the protective polymeric coating is free of reinforcing fibers.

Referring to FIG. 2, carbon fiber composite structural rod 10 includes an inner composite core 12 made from continuous carbon fibers embedded in a polymeric matrix. The protective polymeric coating 24 that surrounds the inner composite core 12 includes randomly oriented, discontinuous non-conductive fibers. In one embodiment, the protective polymeric coating 24 includes about 5 to about 50% by weight of randomly oriented, discontinuous fibers. The discontinuous fibers may be glass fibers, such as one or more of E-glass, D-Glass, E-CR-glass, S-glass, R-glass and S2-glass. In one embodiment, the protective polymeric coating 24 includes about 40% by weight of short glass fibers, and in another embodiment, about 20% by weight of short glass fibers. Other types of discontinuous non-conductive fibers, including ceramic, aramid, liquid crystal polymer and other high temperature polymeric fibers, may be used in the protective outer coating. Referring to FIG. 3, carbon fiber composite structural rod 10 includes an inner composite core 22 made from continuous carbon fibers embedded in a polymeric matrix, and includes a central bore 26. The central bore 26 may be unfilled as illustrated. Alternatively, central bore 26 may be filled with a filler material, such as foam or another non-structural material. The protective polymeric coating 24 that surrounds the inner composite core 22 may include randomly oriented,

discontinuous non-conductive fibers. Alternatively, the protective polymeric coating may be substantially free of fibers as illustrated in FIG. 1 .

The carbon fiber composite structural rod may be used in an electrical transmission conductor. Referring to FIG. 4, electrical transmission conductor 20 includes inner carbon fiber composite core 12, protective coating 14 surrounding the inner core 12, and trapezoidal aluminum or aluminum alloy wires 16 wound around the inner core 12, with the protective coating 14 providing insulation between the inner core 12 and the conductive wires 16. The conductive wires 16 wound around the composite rod may have various cross-sectional geometries, including a circular cross-section. The trapezoidal geometry is preferred as it allows the conductive wires to fit tightly together around the core. The protective coating 14 used in the electrical transmission conductor may or may not include randomly oriented, discontinuous non-conductive fibers.

Example 1

Manufacture of Carbon Composite Core

A carbon fiber composite inner core was produced in a conventional pultrusion process using Zoltek Panex^® 35 carbon fiber together with Momentive RSL-3896 high temperature epoxy resin system and a pultrusion die having a 0.25 inch (6.35 mm) diameter die bore. Eleven (1 1 ) of the 50,000 filament Panex^® 35 tows were impregnated with the RSL-3896 resin system in the pultrusion process and pulled through the heated die for shaping and curing of the composite. The resulting 0.25 inch (6.35 mm) diameter carbon fiber composite rod contained 70% carbon fiber volume fraction and 30% resin volume fraction and zero void content. The certified lot tensile strength of the carbon fiber used was 585,000 psi (4031 MPa). The calculation for estimated maximum load carrying capability of the .025 inch diameter (area = 0.049 inch²) rod is as follows: Fiber strength x Fiber volume fraction = approximate composite strength 585,000 psi x 0.70 = 409,500 psi (2822 MPa) (est. max. composite strength)

Composite strength x Composite cross-sectional area = load capability 409,500 psi x 0.049 inch² = 20,065 pounds (89,254 N) (est. max. load)

The pultruded rod was tensile tested at room temperature using mechanical end fittings in a universal test machine, achieving maximum load at failure of 18,000 pounds (80,068 N) or 90% of theoretical maximum. Further, the rod was tensile tested in the same test configuration with an oven around the test gage to raise the temperature of the rod to 200°C. The resulting elevated temperature maximum load at failure was 15,400 pounds (68,503 N) or 85.5% retention of room temperature property. Example 2

Manufacture of Protective Coating on Carbon Composite Core

A protective polymeric coating was applied to the carbon composite core of Example 1 . The polymer coating containing polyphenylene sulfide (PPS) was applied to the carbon fiber composite inner core using a wire coating process. A ten (10) feet long section of the carbon fiber composite rod was hand fed through a wire coating die attached to an extruder supplying molten PPS to the die. The PPS polymer used was Ryton^® R-4-200, produced by Chevron Phillips Chemical

Company. The PPS polymer contained no fiber reinforcement. The carbon fiber composites rod was lightly abraided with sandpaper and solvent wiped to remove any surface mold release or other contaminants that might prohibit good bonding and to slightly roughen the surface for improved mechanical bonding. In addition, the carbon composite rod was heated as close as possible to the melt temperature of the PPS to promote good wetting of the molten polymer to the composite rod. The resulting coated rod had a uniform protective polymeric coating of 0.035 inch (0.899 mm) thickness. FIG. 5 is a photograph of a cross-section of the carbon fiber rod containing a carbon fiber composite inner core and an outer protective polymeric coating, the coating containing no reinforcing fibers. FIG. 8 is a photograph showing the exterior of the coated carbon fiber composite rod. Example 3

Manufacture of Protective Coating Containing Fibers

A protective polymeric coating was applied to the carbon composite core of Example 1 substantially in accordance with the process of Example 2 with the exception that the PPS contained 40% by weight of short (average length 1 mm) E- glass fibers as fillers. FIG. 6 is a photograph of a cross-section of the carbon fiber rod containing a carbon fiber composite inner core and an outer protective polymeric coating, the coating containing 40% reinforcing fibers. FIG. 9 is a photograph showing the exterior of the coated carbon fiber rod.

Example 4

Manufacture of Protective Coating Containing Fibers A protective polymeric coating was applied to the carbon composite core of

Example 1 substantially in accordance with the process of Example 2 with the exception that the PPS contained 20% by weight of short E-glass fibers as fillers. FIG. 7 is a photograph of a cross-section of the carbon fiber rod containing a carbon fiber composite inner core and an outer protective polymeric coating, the coating containing 20% reinforcing fibers.

The structural core of an electrical transmission cable must have some end fitting that serves as the structural termination point for the cable. In some cases, the cable may need to be spliced to another cable segment. In either case, a mechanical end fitting is used that transfers the load to the termination point or spliced cable segment. A key requirement for the successful use of the carbon rod as a structural reinforcement for high-voltage transmission cables is the ability to transfer load through a mechanical end fitting or termination.

Referring to FIG. 10, the mechanical end fitting 30 is typically a steel clamping device that applies compressive force around the circumference of the rod and over some length of the rod. The tensile load in the rod is transferred to the end fitting 30 through shear forces applied longitudinally at the rod / end fitting interface and the load is transferred from the end fitting to a fixed termination point 32. Testing Load Transfer

To validate the load transfer capability of the polymer coated rod to a mechanical end fitting, the test specimen shown in FIG. 1 1 was tested to failure in a universal test machine. Three specimens produced in accordance with Example 2 were tested with an average failure load of 18,889 pounds (84,022 N) and a standard deviation of 167 pounds (743 N). This represents 94% of the calculated theoretical maximum load carrying capability of the carbon composite rod, clearly validating the load transfer capability of the polymer coating. Subsequent evaluation of the coating inside the mechanical end fitting showed no damage to the coating other than slight compression deformation created by the compression clamping force of the end fitting. A photograph of the section of failed rod that was inside the end fitting is shown in FIG.12.

The structural support rod of the present invention has particular utility for use in electrical transmission cable applications. The structural support rod has other potential applications, including, but not limited to, a reinforcement or structural carrier for underwater cables and tethers for offshore drilling platforms, structural cables for cable stayed bridges, structural cables for sailboat riggings, structural cables for post-tensioned concrete structures, embedded reinforcements in structural concrete structures, and other similar applications.

While the invention has been explained in relation to various embodiments, it is to be understood that various modifications thereof will be apparent to those skilled in the art upon reading the specification. The features of the various embodiments of the articles described herein may be combined within an article. Therefore, it is to be understood that the invention described herein is intended to cover such modifications as fall within the scope of the appended claims.

Claims

What is claimed is:

1 . A core for an electrical conductor comprising:

an inner composite core comprising continuous carbon fibers embedded in a polymeric matrix, the inner composite core being substantially free of continuous fibers different from carbon fibers; and

a protective polymeric coating bonded to and surrounding the inner composite core.

2. The core of claim 1 wherein the polymeric matrix comprises a thermosetting polymer.

3. The core of claim 2 wherein the thermosetting polymer comprises an epoxy.

4. The core of claim 1 wherein the polymeric matrix comprises a thermoplastic polymer.

5. The core of any one of the preceding claims wherein the polymeric coating comprises a thermoplastic polymer.

6. The core of claim 5 wherein the thermoplastic polymer comprises

polyphenylene sulfide

7. The core of any one of claims 1 -4 wherein the polymeric coating comprises a thermosetting polymer.

8. The core of any one of claims 1 -6 wherein the protective polymeric coating comprises a thermoplastic polymer matrix and randomly oriented, non-conductive reinforcing fibers embedded in the thermoplastic polymer matrix.

9. The core of claim 8 wherein the reinforcing fibers comprise glass fibers.

10. The core of any one of claims 1 -7 wherein the protective polymeric coating is substantially free of fibers.

1 1 . The core of any one of the preceding claims wherein the thickness of the protective coating is in the range of about 0.01 inch (0.25 mm) to about 0.1 inch (2.5 mm).

12. The core of any one of the preceding claims wherein the tensile strength of core is at least 250,000 psi (1723 MPa).

13. An electrical conductor comprising:

the core of any one of the preceding claims; and

a plurality of electrically conductive rods wound around the core.

14. The electrical conductor of claim 13 wherein the conductive rods comprise aluminum or an aluminum alloy.

15. A method of forming a core for an electrical conductor comprising:

forming an inner composite core from a plurality of continuous carbon fibers embedded within a resin matrix, the inner composite core being substantially free of continuous fibers different from carbon fibers;

at least partially curing the resin matrix; and

applying a coating of a polymeric material directly to the inner core to form a protective coating surrounding the inner core.

16. The method of claim 15 wherein forming the inner composite core comprises pultrusion.

17. The method of claim 15 wherein applying the coating of polymeric material comprises wire coating.

18. The method of any one of claims 15-17 wherein the polymeric material further comprises randomly oriented, discontinuous nonconductive fibers.

19. The method of any one of claims 15-18 wherein the polymeric material comprises a thermoplastic resin.

20. The method of any one of claims 15-18 further comprising the step of curing the polymeric material to form the protective coating.

21 . A carbon fiber composite structural rod comprising:

22. The composite of claim 21 wherein the polymeric matrix comprises a thermosetting polymer.

23. The composite of claim 22 wherein the thermosetting polymer comprises an epoxy.

24. The composite of claim 21 wherein the polymeric matrix comprises a thermoplastic polymer.

25. The composite of any one claims 21 -24 wherein the polymeric coating comprises a thermoplastic polymer.

26. The composite of claim 25 wherein the thermoplastic polymer comprises polyphenylene sulfide

27. The composite of any one of claims 21 -24 wherein the polymeric coating comprises a thermosetting polymer.

28. The composite of any one of claims 21 -26 wherein the protective polymeric coating comprises a thermoplastic polymer matrix and randomly oriented reinforcing fibers embedded in the thermoplastic polymer matrix.

29. The composite of claim 28 wherein the reinforcing fibers comprise glass fibers.

30. The composite of any one of claims 21 -27 wherein the protective polymeric coating is substantially free of fibers.

31 . The composite of any one of claims 21 -30 wherein the thickness of the protective coating is in the range of about 0.01 inch (0.25 mm) to about 0.1 inch (2.5 mm).

32. The composite of any one of claims 21 -31 wherein the tensile strength of core is at least 250,000 psi (1773 MPa).

33. The composite of any one of claims 21 -32 wherein the inner core includes a continuous central bore.

34. The composite of claim 33, wherein the central bore contains a non-structural filler.

35. The composite of claim 34, wherein the non-structural filler comprises foam.